S.N. Sedgwick, The British Nature Book, Edinburgh, T.C. & E.C. Jack, 1922.

The female lays her eggs in water, and the larvae construct remarkable cases in which to pass the larval and pupal stages. Some use small bits of stick and leaves; others use leaves only, fastening them together by some sticky secretions; another species use sand and small stones; while yet another uses the shells of small water-snails (often with the real owners still Inside).